Permafrost designates the portion of ground that is permanently frozen, at least for two years. Due to the existence of a very cold winter, the cold can penetrate deeply into the sub-soil. During the summer, the low heat does not make it possible to heat the sub-soil throughout its entire depth: certain portions of the sub-soil are as such constantly frozen.
However, if the permafrost thaws (artificially or naturally), the latter becomes unstable because its mechanical properties are modified. For example, the permafrost can be heated due to:
climate warming;
a drilling (mechanical friction of the drill in the sub-soil);
the operation of an existing production well (petrol or production gas being at temperatures higher than 0° C.);
the exothermic reaction of the hardening of concrete/cement (in case, in particular of an installation of a screed of concrete/cement on the ground or for the construction of a production well of which the walls would be cemented);
the simple presence of a building built on the ground, limiting as such the penetration of the cold under the building;
etc.
In the case where the permafrost thaws, any installations/buildings installed on it tend to sink into the sub-soil due to their own weight, as the thawing ground then loses its capacity to resist.
In order to prevent the thawing of the permafrost in the event of the present of a building, certain States have set down construction rules aiming to raise the buildings using piles and as such favour the penetration of the cold into the sub-soil (see for example “Construction Code and Regulation—Base and Foundations on the permafrost soils—SniP 2.02.04-88—USSR State Building and Construction Committee”).
However, these methods do not allow for the construction of all types of buildings (e.g. buildings that must support substantial weights, roads, airport runways, drilling supports, storage zones, etc.).
In addition, these methods do not resolve the issues linked to the supplying of heat from a production well: there are as such risks of losing the confinement or stability for the well or the drilling tools. Some methods have proposed to insulate the well from the sub-soil by adding insulating materials in an annular space of the well. However, the latter are expensive because their insulating power has to be substantial, as the space available for the installation of these insulations is low in a well.
Inversely, in the framework of storing liquefied gases in the ground, it can be sought to prevent the freezing of the sub-soil which could provoke upheaving and damage to the confinement/storage. As such, normally, outside heating systems of the sub-soil are implemented and the walls of the storage structure are covered with an expensive and fragile insulation.
There is as such a need to facilitate the construction of buildings on the ground in permafrost zones and/or to insulate the production wells simply and economically.